Radiation therapy has been one of the three effective treatment modalities in cancer management. it has been a current technical endeavor to further improve radiation treatment efficacy by increasing targeting accuracy, i.e. the delivery of radiation doses directly to the target tumor while limiting the damage/radiation exposure to surrounding healthy tissue. One of the major challenges in this endeavor is the movement or motion of a tumor due to normal respiration during radiation treatment delivery. There have been a number of technologies developed to overcome this challenge. They are notably: respiratory gating; breath holding; and real-time tumor tracking. Of these three techniques, the real-time tumor tracking is considered the most optimal. There are few techniques used for real-time tumor tracking. The most frequently used techniques for real-time tumor tracking involve the use of radio-opaque tumor surrogates (fiducials) such as metallic seeds (e.g. Synchrony Respiratory Tracking System by Accuray, Inc) or radio-frequency transponders (e.g. Calypso® System), which require invasive procedures to implant the surrogates inside or around tumors.
On the other hand, non-invasive techniques for real-time tumor tracking has been actively sought after for treatment of sensitive areas such as the lung, which has historically been challenging. Fiducial-less real-time tracking techniques have been developed and clinically implemented for lung tumors located in selective regions in which radiographical visualization is possible (e.g. Xsight Lung, Accuray, Inc). Fiducial-less real-time motion tracking for abdominal tumors, such as liver tumors and pancreatic tumors, however remains a challenge, where no commercial, practical solution is currently available for clinical use. One of the main contributing factors to the difficulties of fiducial-less motion tracking of abdominal tumors is the inability to visualize abdominal tumors in non-volumetric types of radiographic images. Much like the advent of fiducial-less motion tracking for lung tumors, the present invention describes a new approach for fiducial-less real-time tracking of abdominal tumors.